Aio was a town located in Yoshiki District, Yamaguchi, Japan.
On October 1, 2005 Aio, along with the town of Tokuji, from Saba District, and the towns of Ajisu and Ogōri, all from Yoshiki District, was merged into the expanded city of Yamaguchi.
As of 2003, the town had an estimated population of 7,801 and a density of 323.83 persons per km². The total area was 24.09 km².